Many attempts have been made to produce 3-D motion pictures. The technique generally used involves simultaneously photographing a subject using two motion picture cameras positioned to provide left and right eye views of the subject. The images recorded on films in those cameras are then simultaneously projected onto a screen and are optically coded in some way so that the left eye of a viewer sees only the images that were recorded by the "left eye" camera while the viewer's right eye sees only the "right eye" images. The viewer then perceives a stereoscopic or 3-D effect.
Coding of the images may be effected by the use of what are in effect shuttered spectacles worn by a viewer. The shutters effectively block and unblock the view from each eye alternately in timed relation to projection of the images onto the screen so that the viewer's right eye is blocked when left eye images appear and vice versa. This technique is referred to as "alternate eye" 3-D and is discussed, for example, in U.S. Pat. No. 4,424,529 (Roese et al.).
Spectacular 3-D motion pictures can be made using large format films such as those that are available from Imax Systems Corporation of Toronto, Canada under the registered trade marks IMAX and OMNIMAX. The use of large format films has become possible as a result of development of the so-called "rolling loop" film transport mechanism for cameras and projectors. U.S. Pat. No. 3,494,524 to Jones discloses the principle of a rolling loop transport mechanism. A number of improvements in the original Jones mechanism are disclosed in U.S. Pat. Nos. 3,600,073, 4,365,877 and 4,441,796 (all to Shaw). All of these patents have been assigned to Imax Systems Corporation.
Essentially, the rolling loop mechanism includes a curved stator and a rotor which co-operate to define a passage through which the film is transported. The rotor has gaps in which loops of film are continuously formed as the rotor rotates. Each loop is developed by feeding film from an input sprocket into one of the rotor gaps as the gap travels from a film inlet location to an aperture in the stator. The loop then decays progressively as the gap travels from the aperture to a driven output sprocket. At the position of the aperture the film is held stationary on a registration pin or pins. In a projector, the stationary film is illuminated by a light source and the image is projected onto a screen.
U.S. Pat. No. 3,944,349 (Jones) discloses a focal plane shutter assembly for a rolling loop projector which includes a plurality of curved shutter plates. Each of the gaps in the rotor is bridged by one of the shutter plates so that light passing through the film is cut off as the gap passes the aperture. In the interests of high illumination efficiency, the plates are narrower than the aperture. However, a consequence of this shutter design is that, in alternate eye 3-D projection from two projectors or from a single, double film/double lens projector, portions of both "left eye" and "right eye" images would appear on the screen at the same time. This would seriously detract from the quality of the 3-D image presentation.